libusb: implement zlp flag in libusb transfer

[aokblast]

Summary

The USB protocol defines a Zero-Length Packet (ZLP) to signal the end of
a transfer when the data size is an exact multiple of the Maximum Packet
Size (MPS). Without a ZLP in such cases, the device may not be able to
determine that the transfer has completed.

This flag is added to libusb to allow the user send a ZLP in the end
of libusb_xfer.

[aokblast]

Send packet only the multiple of packet

[aokblast]

defer zlp check until we can find the xfer

[lwhsu]

lib/libusb/libusb10.c

1661

should we use libusb20_tr_get_max_packet_length() or libusb20_tr_get_max_total_length()?

[aokblast]

Get correct MPS

[aokblast]

This implemented is problematic since the correct way is to append a zero size TRB in TD instead of creating new TD. However, I think I am unable to make it work before 15.0 release. Therefore, I will modify it to at least we won't break any ABI for 15 if we want to merge later.

[aokblast]

Use the correct impl